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P0171, searched, troubleshoot, still no dice. Help?

Discussion in 'Generation 1 Prius Discussion' started by mohater, Jan 9, 2022.

  1. mohater

    mohater Junior Member

    Joined:
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    Vehicle:
    2008 Prius
    Model:
    Four
    Another donated prius with some gremlins.

    Recently donated 2001 Prius, 220k on the odo, came with P0171 CEL. Drove it 200 miles. vehicle never misfired, but CEL present and short/long term trim staying too far apart. Reset CEL, drove 20 mins, was ready for California SMOG, smogged it w/o turning if off (figured out the gen 1 prius won't trip the CEL if you leave it on and finish the drive cycle in one shot), passed. Drove off after tech turned car off and I turned back on, and 5 mins later CEL tripped.

    The vehicle recently misfired on a warm start for like 20 seconds, then it cleared up. Cylinder 1 and 3. No service history with the car.

    Browsed here, cleaned the MAF, cleaned the intake, no difference in short/long term trim. Checked vacuum hoses, don't appear to be any leaks. O2 sensors voltage fluctuations look normal ( from 0.1 to 0.9 something).

    Wanted to inquire before I just start ordering parts. I was thinking replace plugs as a starting point, and probably just replacing all the vacuum lines since they might be original.

    Any other thoughts? Thanks!
     
    #1 mohater, Jan 9, 2022
  2. TMR-JWAP

    TMR-JWAP Senior Member

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    Can you describe how you cleaned the MAF sensor?
     
    #2 TMR-JWAP, Jan 9, 2022
  3. mohater

    mohater Junior Member

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    Four
    Removed the MAF, used the electronics/MAF cleaner on the sensor tip. It wasn't mucked up or black, could clearly see the silver metal. Let it dry for a few mins, returned to the intake.

    Cleaned the intake with intake cleaner, sprayed the outside of the port (closed), opened and sprayed the other side and the area around the throttle plate, used a clean rag/shop towel to wipe off.

    Let everything dry for 10-15 mins, started car back up. Very little hesitation upon start (normally a little rough start after cleaning MAF and throttle body).
     
    #3 mohater, Jan 10, 2022
  4. TMR-JWAP

    TMR-JWAP Senior Member

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    When I had the P0171 on my Gen 2, the first time I "cleaned the MAF", I only cleaned the temperature sensing bulb due to a misunderstanding. When I later cleaned the sensor wire inside the housing, I did similar to your description and just sprayed it well with cleaner. Unfortunately, I continued getting codes on and off. I then cleaned it again, but this time, used the cleaner to wet a q-tip and reached down inside the sensor to gently rub the element. I was very surprised how dirty it came out. I was extremely careful, but also had a spare MAF on the shelf in case I bent the sensor/heating wire. No more codes since then.
     
    #4 TMR-JWAP, Jan 10, 2022
    Gary Seven likes this.
  5. mohater

    mohater Junior Member

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    Location:
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    2008 Prius
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    Four
    Thanks! Will try that next when I go wrench on the car (next weekend).
     
    #5 mohater, Jan 10, 2022
  6. Gary Seven

    Gary Seven New Member

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    I
    Thanks for this post. I was fighting the P0171 code for months. Turned out I bought a "new Denso" MAF on Ebay when I first got the fault code and it was bad. So I cleaned my old MAF very carefully with a Q-tip, it was very dirty, and my long term fuel trim came way down and the fault finally cleared. I will only use Denso parts from a reputable source from now on.
     
    #6 Gary Seven, May 2, 2022
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